1. Field of the Invention
The present invention is directed to current comparators, particularly to a current comparator which makes use of cross-coupled current copiers to perform two comparisons of the reference and the signal currents.
2. Description of the Prior Art
Recently, current mode circuits have been the subject of much research. This is due to their potential to operate faster that their equivalent voltage mode circuits and the fact than the voltage swing on the internal nodes is small. Thus, current mode circuits tend to generate less noise than their voltage counterparts and can be used in applications with lower supply voltages.
A number of current mode ADCs have been designed and published in the prior art. The central comparison performed in these ADCs is to use current mirrors or current copiers to supply the reference and signal currents. A current to voltage conversion is carried out at the high output impedance of the current mirrors or current copiers, followed by some voltage detection and amplification.
However, these prior art comparators suffer from the significant drawback that in these systems one of the mirrors is connected to the power supply, while the other is connected to the ground supply. Consequently, any noise present on one of the supplies but not the other may affect the comparison, reducing the efficiency of the circuit.
An improved current comparator is therefore needed which significantly reduces the supply noise rejection problem while maximizing the overall gain of the circuit.